A private art gallery in Moscow has hastily closed down an exhibition of pictures by US photographer Jock Sturges after a pro-Kremlin senator labelled them child abuse images and a protester threw urine at some of the images.

Sunday’s incident at the Lumiere Brothers Center for Photography, a stone’s throw from the Kremlin, followed a series of earlier attacks by Russian Orthodox believers and nationalists on displays of modern art.

Senator Yelena Mizulina said the photo exhibition included images of naked school-age girls and therefore qualified as child abuse. “This is propaganda of paedophilia in the most accurate sense of the word,” she said in comments cited by state television.

Nearly two dozen activists from a little-known non-governmental organisation called ‘Officers of Russia’ stand outside the doors of the Lumiere Brothers gallery. Photograph: Andrei Borodulin/AFP/Getty Images

Anna Kuznetsova, presidential ombudsman for children’s rights, called for an investigation of the exhibition by prosecutors. Kremlin spokesman Dmitry Peskov declined comment.

Sturges, 69, is described in one of his biographies as a “lightning rod for controversy” for his brand of nude photography, which has also got him into trouble in the United States. Investigators raided his home and studio in 1990 but a grand jury decided not to indict him.

In comments to Russia’s REN TV, Sturges said his pictures of about 25 families, taken over a few decades, had nothing to do with pornography. They had been shot with the consent of the models or, if they were under-age, of their parents.

On Sunday the exhibition was stormed by a group of men from Officers of Russia, a public organisation which says it unites more than 100,000 veteran and active officers and its main aim is the “patriotic upbringing of the population”.

Several television channels showed a man throwing liquid at the pictures from a plastic bottle. The TV channels reported it was urine.